package leetcode.D100.T96;

public class Solution {
    // 一刷
    /*public int numTrees(int n) {
        int[] G = new int[n+1];
        G[0] = G[1] = 1;
        for(int i=2; i<=n; ++i) {
            for(int j=1; j<=i; ++j) {
                G[i] += G[j-1] * G[i-j];
            }
        }
        return G[n];
    }*/

    // 二刷
    public int numTrees(int n) {
        int[] dp = new int[n+1];
        dp[0] = dp[1] = 1;
        for (int i=2; i<=n; ++i) {
            for (int j=0; j<i; ++j) {
                dp[i] += dp[j] * dp[i-j-1];
            }
        }
        return dp[n];
    }
}
